Electrochemical cells, and gas sensor and fuel cell devices comprising same

ABSTRACT

An electrochemical cell for applications such as electrochemical fuel cells, or electrochemical cell gas sensors used for detection of target gas species in environments containing or susceptible to presence of same. The electrochemical cell utilizes an ionic liquid as an electrolyte medium, thereby achieving a broader range of operational temperatures and conditions, relative to electrochemical cells utilizing propylene carbonate or other conventional electrolytic media.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/451,538 filed Jun. 12, 2006; which is a divisional of U.S. patentapplication Ser. No. 10/218,262 filed Aug. 14, 2002 in the name ofAndreas Rohrl for “Electrochemical cells, and gas sensor and fuel celldevices comprising same,” which issued on Jun. 13, 2006 as U.S. Pat. No.7,060,169, the entirety of each which is incorporated herein byreference for all purposes.

BACKGROUND

1. Field of the Invention

The present invention relates generally to electrochemical cells and todevices incorporating same, such as fuel cells, sensors, andelectrochemical cell gas sensors used for detection of gases inenvironments containing or susceptible to presence of same, and in aspecific aspect, the invention relates to an electrochemical cellutilizing ionic liquid as an electrolyte medium thereof.

2. Description of the Related Art

Gas sensors are used in many commercial and industrial applications,including workplace monitoring for the presence of toxic or otherwisehazardous or deleterious gases and in other applications where healthand safety issues require detection of specific gases in the ambientenvironment.

In these various applications, it is frequently necessary or desirableto monitor concentration of selected gas species down to levels on theorder of a few parts per million and less.

Gas sensors used in the foregoing applications include electrochemicalgas sensors, which may operate to electrochemically reduce the gasspecies to be monitored. Alternatively, the gas sensor may operate byelectrochemically oxidizing the target gas species sought to bedetected. As a still further alternative, the electrochemical gas sensormay operate by indirect oxidation or reduction reaction of a compoundthat is produced in the gas sensor device, involving the target gas tobe detected in the monitored gaseous environment.

Electrochemical gas sensors utilize sensor cells that typically containthree electrodes—the working electrode, the reference electrode and thecounter electrode, although gas sensor cells are known having2-electrode and 4-electrode structures. The electrodes areconventionally mounted within a housing that additionally contains anelectrolyte, contacts and electrical wires forming electronic circuitryof the sensor, and a gas permeable membrane that keeps the electrolytewithin the cell and allows the gas to contact the measuring electrode.

Electrochemical sensor cells require an electrolyte as a component ofthe electrochemical cell. The electrolyte performs the transport ofelectrical charge between the different electrodes and therefore enablesan electrical current to flow. The transport of electrical charge by theelectrolyte is ionic in character rather than involving charge transportby electrons.

The electrolyte usually is constituted by a liquid solvent containingelectrolyte/salt component(s), wherein the solvent comprises water, oralternatively a non-aqueous solvent medium, but the electrolyte mayotherwise comprise a solid electrolyte such as yttrium-stabilizedzirconia (YSZ) for usage at high temperatures of about 450 to 950° C. oran ion exchange membrane such as a Nafion® membrane (commerciallyavailable from DuPont de Nemours and Company, Wilmington, Del.) that issaturated with water.

Liquid electrolytes in some instances can be ‘solidified’ by additionthereto of gel-forming agents, but the resultantly solidifiedelectrolyte materials still rely on the presence of liquid solventmedium for operability, as do ion exchange systems such as the ionexchange membranes mentioned above.

Gas sensors are operationally “open systems” in the sense of requiringgas flow therethrough for detection of gas component(s) in the gasstream with which the gas sensor is contacted. One major deficiency ofconventional gas sensors is the limited service life of liquidelectrolytes that include gels or wetted membranes, since thesematerials dry out over time as solvent evaporates therefrom.

Water-based gas sensor systems are designed to be in equilibrium withambient humidity of the environment being monitored, but their utilityis generally restricted to a specific humidity range.

Solid electrolyte gas sensors are difficult to construct for efficientoperation, since diffusion of gas in the solid electrolyte material ishindered in relation to liquid electrolytes, there is no transport ofreactants in the solid electrolyte, and known solid electrolytematerials tend to be hygroscopic and thus are difficult to stabilize inhumid environments. Additionally, solid electrolytes (i.e. solidmaterials providing intrinsic ion transport by usually oxide ions O²⁻)need high operating temperatures. For example, yttrium-stabilizedzirconia (YSZ) used in oxygen sensors does not provide sufficient ionconductivity at temperatures below 450° C.

The art therefore continues to seek improvements in electrochemical cellgas sensors.

SUMMARY OF THE INVENTION

The present invention relates generally to electrochemical cells, forapplications such as electrochemical energy supplies (fuel cells,batteries, etc.) and electrochemical cell gas sensors.

In one aspect, the invention relates to an electrochemical cellincluding an electrolyte therein in electrical contact withelectrochemical cell electrodes, wherein the electrolyte comprises anionic liquid.

In another aspect, the invention relates to a method of increasingperformance of an electrochemical cell, comprising using in such cell anelectrolytic medium including an ionic liquid electrolyte.

Other aspects, features and advantages of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a process system employing anelectrochemical cell gas sensor according to the present invention, inan illustrative embodiment thereof;

FIG. 2 is a schematic representation of an electrochemical cell gassensor and filter unit according to one embodiment of the invention; and

FIG. 3 is a simplified schematic representation of an electrochemicalfuel cell according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

The present invention relates to electrochemical cells utilizing ionicliquids as electrolyte media.

As used herein, the term “ionic liquid” means a salt comprising at leastone cation and one anion and being liquid at temperatures below 250° C.,preferably below 100° C., and most preferably below 50° C. (e.g., 20-30°C.).

The ionic liquids employed in the broad practice of the invention may beof any suitable type, and include those disclosed in: InternationalPublication No. WO 00/16902 for “IONIC LIQUIDS;” InternationalPublication No. WO 00/15594 for “PROCESS FOR MAKING AROMATIC ALDEHYDESUSING IONIC LIQUIDS;” U.S. Pat. No. 4,554,383; Seddon, K. R., MoltenSalt Forum, 5-6, pp. 53-62 (1998); and Seddon, K. R., Kinetics andCatalysts, 37, 5, pp. 743-748 (1996), the disclosures of which herebyare incorporated herein by reference in their respective entireties.

The electrochemical cell devices of the present invention includeelectrochemical cell gas sensors and fuel cells, wherein ionic liquid isemployed as an electrolyte medium, having utility in many environmentsincluding but not limited to:

-   -   a) environments having broad humidity range, preferably        environments having low relative humidity;    -   b) environments having high air flow; and    -   c) environments operating at higher temperatures.

Additionally, the electrochemical cell devices of the present inventioninclude electrochemical cell gas sensors, having potentially smallerphysical dimensions as compared to current electrochemical cell gassensing devices using aqueous and organic solvent electrolyte. Suchsmaller dimensions are possible, because unlike current electrochemicalsensors, solvent evaporation issues are substantially non-existentallowing for reduced amounts of electrolyte and elimination ofreservoir(s) for solvent replacement.

By minimizing the evaporation issue, the electrochemical cell gassensors of the instant invention are advantageously available fordetecting a broader range of target compounds and sensor lifetime is nolonger restricted by the amount of electrolyte.

In one aspect, the electrochemical cell of the invention comprises anelectrochemical cell gas sensor, in which an ionic liquid is employed asan electrolyte. The electrochemical cell gas sensor may be of anysuitable fabrication or construction, e.g., comprising a housing, withtwo or more electrodes operatively arranged in an interior volume of thehousing and communicating with electrical circuitry means (e.g.,contacts, wires, conductive films, circuit components, etc.) and theionic liquid electrolyte.

The ionic liquid may be of any suitable type and may have a meltingpoint that is ≦250° C. The melting point of the ionic liquid may beabove or below the operating temperature of a particular process.

The vapour pressure of the ionic liquids of the instant invention atroom temperature is negligible to non-measurable, as compared toelectrolyte materials of the prior art (such as water, acrylonitrile,propylene carbonate, and the like).

Illustrative ionic liquids useful as electrolyte materials inelectrochemical cell gas sensors in the practice of the presentinvention include, without limitation, salts with imidazolium orpyridinium cations. The cations that may be usefully employed in a givenapplication of the invention include cations with alkyl and/or arylsubstituents, optionally wherein the alkyl and/or aryl substituents arethemselves further substituted, e.g., with halo, loweralkyl (C₁-C₄),hydroxyl, amine, etc.), such cations being capable of forming salts whenreacted with corresponding anions.

Illustrative anions for such purpose include, without limitation,halides (chlorides, iodides, bromides, fluorides), nitrates, nitrites,tetrafluoroborates, hexafluorophosphates, trifluoromethanesulfonates andother polyfluoroalkanesulfonates, e.g., nonaflate,bis(trifluoromethylsulfonyl)imides, methylsulfates, acetates,fluoroacetates and other anions of fluoroalkanoic acid.

In one embodiment, the ionic liquid electrolyte comprises at least onesalt selected from the group consisting of salts with the generalformula C⁺A⁻ where C⁺ represents a quaternary ammonium and/orphosphonium salt and A⁻ represents any known anion that can form ionicliquids in the meaning described in the present invention. Non-limitingexamples include methyl-octyl-imidazolium-chloride andbutyl-methyl-imidazolium-bis-trifluoromethane-sulfonimide.

The low vapour pressure ionic liquids in gas sensor electrochemicalcells of the present invention may include compounds as described above,in single salt electrolyte compositions, as well as use of same andsimilar compounds in mixtures together with varying amounts of aluminumhalides, preferably aluminum chloride, or other salts that increase theconductivity of the electrolytic medium, or otherwise enhance the gasdetection sensitivity of the gas sensor electrochemical cell.

The electrochemical cell gas sensor of the invention may be constructedand arranged in any appropriate manner to carry out the sensing of thetarget gas species in a gaseous environment containing or susceptible tothe presence of same. The fabrication and manufacture of electrochemicalcell gas sensors is more fully described in Advances in Electrochemistryand Electrochemical Engineering, Volume 10, John Wiley & Sons, 1976, andthe electrochemical cell gas sensor assembly in accordance with theinvention may include a chemically selective filter for theelectrochemical gas sensing cell, to remove interferent gas componentsthat would otherwise interfere with or preclude measurement of thetarget gas species in the gas environment being monitored by the gassensor assembly.

For example, the electrochemical cell gas sensor may be constructed andarranged to electrochemically reduce the gas species to be monitored, sothat the monitoring operation involves chemical reduction of the targetgas species. Alternatively, the electrochemical cell gas sensor mayoperate by electrochemically oxidizing the target gas species sought tobe detected. As a still further alternative, the electrochemical cellgas sensor may operate by indirect oxidation or reduction reaction of acompound that is produced in the gas sensor device, involving the targetgas to be detected in the gas environment being monitored for thepresence of the target gas species.

The electrochemical cell gas sensor may be configured to utilize a gassensor cell containing three electrodes—the working electrode, thereference electrode and the counter electrode, although gas sensor cellshaving 2-electrode and 4-electrode structures may alternatively beemployed. The electrodes are mounted within a housing containing theionic liquid electrolyte, with the electrodes being coupled incircuit-forming relationship with contacts and electrical wires formingthe electronic circuitry of the sensor.

The superiority of the ionic liquid electrolyte medium in theelectrochemical cell gas sensor of the present invention has beendemonstrated by relative weight loss tests in which propylene carbonate,a widely used electrolyte of prior art electrochemical cell gas sensors,and ionic liquids of the present invention (e.g.methyl-octyl-imidazolium-chloride andbutyl-methyl-imidazolium-bis-trifluoromethane-sulfonimide) wereevaluated at 80° C. After only 5 days at such temperature of 80° C.,propylene carbonate, having a boiling point of 240° C., was totallyevaporated, while the ionic liquids of the present invention were ofunchanged mass within the accuracy of the measurement apparatus. Theseresults evidence an unexpected advantage and superiority of the ionicliquids of the present invention over electrolyte characteristic ofprior art electrochemical cell gas sensors.

In general, useful electrolytes for electrochemical cells must have anelectrical conductivity of at least 10⁻⁵ ohm⁻¹ cm⁻¹. The electricalconductivity of the ionic salts of the present invention are typicallyon the order of 0.01 ohm⁻¹ cm⁻¹, three orders of magnitude above suchelectrolytic threshold, providing unexpectedly superior performance ofelectrochemical cell gas sensors utilizing same. In general, ionicliquids which are preferred for use as electrolyte in the practice ofthe present invention have an electrical conductivity of at least 10⁻³ohm⁻¹ cm⁻¹ and such ionic liquids most preferably include those havingan electrical conductivity of at least 10⁻² ohm⁻¹ cm⁻¹.

The invention therefore provides an electrochemical cell gas sensorincluding a gas sensor cell in which an ‘ionic liquid’ is employed as anelectrolyte, e.g., a salt having a melting point below 100° C. andpreferably a liquid at room temperature. In contrast to prior artliquids used as electrolyte media, the ionic liquid systems of theinvention are characterized by negligible vapour pressure of theelectrolyte, and an extremely high electrolytic character since theionic liquids are constituted by ions.

In another aspect, the invention provides electrochemical fuel cellsusing ionic liquids as solvent/electrolyte media.

Fuel cells are electrochemical cells consisting of two electrodesconnected with an ion-conducting electrolyte. The electrodes usuallyhave a porous structure and are designed to allow very close contactbetween a gas (the fuel), the electrolyte and the catalyst powder thatcatalyses the chemical reactions. Oxidation and reduction are separatedso that they occur at different electrodes, and the electric circuit isclosed by ion transport from one electrode through the electrolyte tothe other electrode.

The fuel cells of the present invention in one aspect thereof may befabricated with cathode and anode elements in an assembly in which theionic liquid electrolyte medium is disposed between the respectiveelectrodes, in an electrolyte/electrode assembly, with the respectivecathode and anode elements have backing layers on their outer surfacesproviding pathways for gas access to the respective electrode. On theouter surfaces of the respective backing layers are provided currentcollector plates including a cathode current collector plate on thecathode-backing layer, and an anode current collector plate on theanode-backing layer. The current collectors are in turn coupled withcircuitry including load or output device(s) that utilize the electricaloutput of the fuel cell.

In contrast to conventional fuel cells that utilize electrolytes thathighly restrict the operating range of temperature of the fuel cell(e.g., phosphoric acid fuel cells (PAFCs), using phosphoric acid aselectrolyte and operated at about 200° C.; molten carbonate fuel cells(MCFC), using molten carbonates as electrolyte and operated at 500 to600° C.; solid polymer membrane fuel cells (SPMFC), using conductingpolymers as electrolyte and operated below 80° C.; alkaline fuel cells(AFC), using concentrated alkalai brine and operated below 100° C.; andsolid oxide fuel cells (SOFC) operated at temperatures close to 1000°C.), fuel cells utilizing ionic liquid electrolytes in accordance withthe present invention can operate at substantially lower temperaturesand over significantly wider temperature ranges in which the performanceof the prior art fuel cells would be deficient or even non-existent.

The ionic liquids used as electrolyte media in fuel cells of the presentinvention may be of any suitable type, including the ionic liquidelectrolytes described hereinabove in the preceding discussion ofelectrochemical cell gas sensors utilizing ionic liquid electrolytes inaccordance with the present invention.

The features and advantages of the present invention are more fullyappreciated with respect to the following embodiments, described inreference to the drawings.

FIG. 1 is a schematic representation of a process system 10 employing anelectrochemical gas sensor according to the present invention, in anillustrative embodiment thereof.

The FIG. 1 process system 10 includes a supply 12 of a source gas. Thesupply 12 may include a process unit that generates the target gas(i.e., the gas component to be monitored by the electrochemical cell gassensor) in mixture with other gas components, as a multicomponent gasmixture. Alternatively, the supply 12 of the source gas may be a gasenvironment that is subject to ingress or contamination by the targetgas, e.g., as a toxic, or otherwise hazardous or undesirable gas speciesin the particular environment. The source gas, containing the target gasas a component thereof, flows from supply 12 in line 14 to the abatementprocessing unit 16 in which the source gas is treated to remove thetarget gas therefrom.

A target gas-depleted stream is discharged from the abatement-processingunit 16 in line 18, and may be passed to a further downstream process orfinal disposition, as required.

A side stream of the source gas from line 14 is flowed in line 20, underthe action of motive fluid driver 22, through dust filter 23,interferent species filter 24 and gas sensor 26, being returned to line14 downstream of gas sensor 26, as shown. The dust filter 23 removesparticulates from the source gas, and the interferent species filter 24removes gas components from the dust-depleted source gas that mayinterfere with the accurate sensing of the target gas by theelectrochemical cell gas sensor. By this arrangement, aninterferent-free gas composition, including the target gas species, isflowed from the interferent species filter 24 to the electrochemicalcell gas sensor 26.

The electrochemical cell gas sensor 26 monitors the concentration of thetarget gas species in the side stream and generates a correspondingresponse signal correlative to the sensed concentration of the targetgas species. The response signal is transmitted in signal transmissionline 28 to central processing unit (CPU) 30, which in turn generates acorresponding control signal that is transmitted in control signal line32 to the abatement-processing unit 16. The control signal in line 32may be employed to modulate the gas processing operation in abatementprocessing unit 16 to abate the target gas species.

As an illustrative example, if phosgene were the target gas species inthe source gas, and such target gas species is abated by chemicalreaction thereof with a chemical reagent in the abatement processingunit 16, the amount of the chemical reagent may be modulated in responseto the sensed concentration of the phosgene in the source gas, to effectsubstantially complete removal of the phosgene from the gas streamtreated in abatement processing unit 16. In other abatement operations,the process conditions (e.g., temperatures, pressures, flow rates,retention time, etc.) in the abatement processing unit 16 may bemodulated to effect the desired reduction in the concentration of thetarget gas species in the effluent stream being treated.

FIG. 2 is a schematic representation of an electrochemical cell gassensor 50 according to one embodiment of the invention.

The electrochemical cell gas sensor 50 comprises a housing 52 formed ofa suitable material of construction, e.g., metal, ceramic, polymer, etc.defining therewithin an interior volume. The interior volume of thehousing includes an electrolyte compartment 53 containing an ionicliquid electrolyte in accordance with the invention, and an electrodeassembly including a counter electrode 54, a reference electrode 58 anda working electrode 62. The counter and reference electrodes areseparated by separator member 56, and the reference and workingelectrodes are separated by separator member 60.

Overlying the electrode assembly is an interferent species filter 64 forremoving interferent species from the source gas flowed therethrough. Adust filter 66 is joined to the housing 52 at the upper end of thehousing walls, as shown, being sealed to the top edges of the walls bybond 68. The bond 68 is formed of a suitable adhesive or sealant medium,and joins the dust filter 66 to the housing 52 in a leak-tight manner,so that source gas flowed through the filter enters the interferentspecies filter 64 and is prevented from bypassing the filtration andsensing elements in the housing interior volume.

It will be recognized that the electrochemical cell gas sensor 50 isschematically illustrated for ease of description, and does not show theelectrical leads to the electrode elements in the housing or otherancillary structure, but based on such description, the electrochemicalcell gas sensor 50 may be readily constructed by those skilled in theart, to effect gas sensing operation that is accurate and reproduciblefor monitoring of the target gas species in the source gas.

FIG. 3 is a simplified schematic representation of an electrochemicalfuel cell 100 according to another embodiment of the invention.

The electrochemical fuel cell 100 as illustrated includes an ionicliquid electrolyte compartment 108 containing an ionic liquidelectrolyte 102 in accordance with the present invention, and arrangedso that the ionic liquid electrolyte in the electrolyte compartment 108is in contact with anode 106 and cathode 104.

On the outer surface of the anode (the main surface opposite the surfacein contact with the electrolyte) is disposed an anode backing layer 116.In like manner, the outer surface of the cathode 104 has disposed incontact therewith a cathode-backing layer 110.

Outwardly of the backing layers 116 and 110 is provided an anode currentcollector 118 in contact with the anode backing layer 116, and a cathodecurrent collector 112 in contact with the cathode backing layer 110, asshown.

The backing layers 116 and 110 are formed of suitable material havingpathways therein for gas access to the corresponding electrode withwhich the backing layer is in contact.

The anode current collector 118 is formed with fuel flow passages 120therein, accommodating flow of fuel into the passages 120 in thedirection indicated by arrow C, with the spent/unused fuel beingdischarged from such passages in the direction indicated by arrow D. Thefuel may comprise hydrogen or any other fuel medium.

The cathode current collector 112 is correspondingly formed with oxidantflow passages 114 therein, into which oxidant is flowed in the directionindicated by arrow A in FIG. 3, and from which spent/unused oxidant isdischarged in the direction indicated by arrow B. The oxidant may be ofany suitable type, e.g., oxygen, air, oxygen-enriched air, ozone, etc.

The anode and cathode current collectors 118 and 112 in the FIG. 3 fuelcell are coupled with electrical circuitry, schematically represented inFIG. 3 by circuit wire 122, interconnecting the fuel cell with a load oroutput device 124 of desired type.

The fuel cell structure shown in FIG. 3 is highly simplified incharacter for purposes of illustration, and it will be appreciated thatfuel cell apparatus in accordance with the present invention may befabricated and arranged in a wide variety of conformations andembodiments. The fuel cell apparatus may include a fuel cell stackutilizing a plurality of fuel cell unit structures as shown in FIG. 3,joined together with bipolar current collector plates and end plates, asis known in the art for achieving economies of scale in use of fuel cellelements.

The features, aspects and advantages of the present invention arefurther shown with reference to the following non-limiting examplesrelating to the invention.

EXAMPLES Example 1

An electrochemical cell gas sensor, comprising a gas sensor such asschematically described above, allows for the measurement of hydrogensulfide (H₂S) concentrations in a gas mixture. The sensor comprises ameasuring electrode made of silver (Ag), a reference electrode made ofsilver (Ag), and a counter electrode made of silver (Ag). Further, thesensor comprises an electrolyte consisting of an ionic liquid, namelyethyl-methyl-imidazolium-trifluorormethane-sulfonate. Concentrations of20-ppm hydrogen sulfide give rise to a signal current of 0.01 mA. Theresponse time is typically less than 30 s after initial exposure to thegas.

Example 2

An electrochemical cell gas sensor, comprising a gas sensor such asschematically described above, allows for the measurement chlorine (Cl₂)concentrations in a gas mixture. The sensor comprises a measuringelectrode made of gold (Au), a reference electrode made of platinum(Pt), and a counter electrode made of platinum (Pt). Further, the sensorcomprises an electrolyte consisting of an ionic liquid, namelybutyl-methyl-imidazolium-bis-trifluoromethane-sulfonimide.Concentrations of 1-ppm chlorine give rise to a signal current of 0.2μA. The response time is typically 30 s after initial exposure to thegas.

Although the invention has been variously disclosed herein withreference to illustrative embodiments and features, it will beappreciated that the embodiments and features described hereinabove arenot intended to limit the invention, and that other variations,modifications and other embodiments will suggest themselves to those ofordinary skill in the art. The invention therefore is to be broadlyconstrued, consistent with the claims hereafter set forth.

What is claimed is:
 1. An electrochemical gas sensor assemblycomprising: a housing; a first and a second electrode positioned withinthe housing; a substantially solvent-free, ionic liquid electrolytecontained within the housing in electrical contact with the electrodes;and a gas access port, wherein the substantially solvent-free, ionicliquid electrolyte comprises methyl-octyl-imidazolium-chloride, orbutyl-methyl-imidazolium-bis-trifluoromethane-sulfonimide, or mixturesthereof, wherein the substantially solvent-free, ionic liquidelectrolyte is substantially free of additives wherein the substantiallysolvent-free, ionic liquid electrolyte is weight-stable after remaining5 days at a temperature of 80° C.
 2. The electrochemical gas sensorassembly according to claim 1, wherein the substantially solvent-free,ionic liquid electrolyte comprises at least one salt having a meltingpoint less than about 100° C.
 3. The electrochemical gas sensor assemblyaccording to claim 1, wherein the substantially solvent-free, ionicliquid electrolyte comprises one salt.
 4. The electrochemical gas sensorassembly according to claim 1, wherein the substantially solvent-free,ionic liquid electrolyte comprises a mixture of salts.
 5. Theelectrochemical gas sensor according to claim 1, wherein thesubstantially solvent-free, ionic liquid electrolyte has a negligiblevapor pressure.
 6. The electrochemical gas sensor according to claim 1,wherein the ionic liquid electrolyte has an electrical conductivity ofat least 10⁻³ ohm⁻¹ cm⁻¹.
 7. The electrochemical gas sensor assemblyaccording to claim 1, wherein the ionic liquid electrolyte has anelectrical conductivity of at least 10⁻² ohm⁻¹ cm⁻¹.
 8. Theelectrochemical gas sensor assembly according to claim 1, wherein theionic liquid electrolyte further comprises an aluminum halide.
 9. Theelectrochemical gas sensor assembly according to claim 1 furthercomprising a three-electrode arrangement including a working electrode,a reference electrode and a counter electrode.
 10. The electrochemicalgas sensor assembly according to claim 1 further comprising afour-electrode arrangement.
 11. An electrochemical gas sensor assemblyhaving a housing comprising: a substantially solvent-free, ionic liquidelectrolyte, and at least a first and a second electrode in contact withthe ionic liquid electrolyte, wherein the substantially solvent-free,ionic liquid electrolyte comprises methyl-octyl-imidazolium-chloride, orbutyl-methyl-imidazolium-bis-trifluoromethane-sulfonimide, or mixturesthereof, wherein the substantially solvent-free, ionic liquidelectrolyte is substantially free of additives wherein the firstelectrode has a backing layer thereon providing passageways therein forgas access there, wherein the second electrode has a backing layerthereon providing passageways therein for gas access thereto, whereinthe ionic liquid electrolyte is weight-stable after 5 days at atemperature of 80° C.